Why won't bash support !(...) patterns when executed via make (w/ SHELL:=/bin/bash)?

Question

I have a problem running a line of code in my Makefile that runs well in /bin/bash. I know that Make runs in /bin/sh so I have solved that problem with this guide by declaring to Make that I want it to run in Bash. However, even though I run Make in Bash I still cant get this line to work, even tough it works in Bash just fine.

Why does Bash throw an error when running rm -f !(2).txt in the Makefile but not when executed out in its shell?

EDIT: I seek to delete all files with a certain file extension except one of those files. The command rm -f !(2).txt does just that in my bash terminal but not in Make.

EDIT: When running rm -f !(2).txt "normally" in the terminal with Bash (terminal returned bash when issuing command echo "$0") it works just fine but whey I run /bin/bash -c 'rm -f !(2).txt' I get the same error as in the Makefile.

Makefile

all: clean

clean: SHELL:=/bin/bash
clean:
    rm -f !(2).txt

Running command in Bash

 $ ls
1.txt  2.txt  3.txt  4.txt  Makefile    # Directory has all text files
 $ rm -f !(2).txt                       # Remove all text files but 2.txt
 $ ls
2.txt  Makefile                         # Only 2.txt is not removed

Running command in Bash through Makefile

 $ ls                                   # Directory has all text files
1.txt  2.txt  3.txt  4.txt  Makefile
 $ make clean                           # Running make 
rm -f !(2).txt
/bin/bash: -c: line 0: syntax error near unexpected token `('
/bin/bash: -c: line 0: `rm -f !(2).txt'
make: *** [clean] Error 1

Answer 1

You need to enable the extglob shell option in order to make it work. In GNU make, it can be achieved by

SHELL := /bin/bash
.SHELLFLAGS := -O extglob -c

---

Edit by question author

The example with the two rows of code above did not work for me but as this fellow found out, there seems to be a different solution depending on versions.

Hmm. For some reason the .SHELLFLAGS didn't work for me, but putting the flags directly in SHELL=/bin/bash -O extglob -c did. [...] – Timothy Jones

The example @choroba uses works in Make 4.0 but did not work for me since I have Make 3.81. However, here is my solution:

all: clean

clean: SHELL=/bin/bash -O extglob -c
clean:
    rm -f !(2).txt

Answer 2

Make has no idea what "!(2).txt" means, if you really must use this construct, then use the $(shell) function:

%(shell rm -f !(2).txt)

Personally, I would change your file naming scheme or build the file names you want to delete in a make variable.